1. Field of the Invention
The present invention relates to a measurement process and device applicable to packet-switched data transmission networks, and in particular to those known by the abbreviation ATM "asynchronous transfer mode".
2. Discussion of the Background
The packets transported in ATM networks are referred to as cells and it may be beneficial to know, at a point of a stream of cells, what is, at each instant, the proportion of cells which satisfy a specified criterion: for example, what is the proportion of cells corresponding to a given connection, to a given service, etc.
If the total rate of the stream of cells is known, as is for example the case when dealing with the stream of ATM cells travelling along a highway with a known bit rate, a measurement of proportion makes it possible to deduce a measurement of bit rate in respect of the cells satisfying the relevant criterion.
In actual essence, such a measurement should give a result at any instant but it should take account of events which have happened in a more or less recent past. A simple sliding average, such as described in patent application WO-A-94/11972, may suffice in numerous cases but the implementation of such an algorithm generally calls upon a circular queue of the latest values, this requiring capabilities for storage and for indexed access to the memory. Moreover, the horizon of this average, that is to say its capacity to store the past depends directly on the physical memory available.